Problem: $ { {1} \times \left[\begin{array}{rr}{3} & {4} \\ {1} & {-1} \\ {-2} & {1}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{1}\times{3} & {1}\times{4} \\ {1}\times{1} & {1}\times{-1} \\ {1}\times{-2} & {1}\times{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{3} & {4} \\ {1} & {-1} \\ {-2} & {1}\end{array}\right]}$